Project Summary: Significance: HCV incidence is increasing among young, non-urban PWID, consistent with the shifting epidemiology of drug use in the US. However, HCV-related mortality is mainly among an aging population of former PWID, infected when HCV incidence peaked in the 1990s, and can be accelerated by HIV. Furthermore, upwards of 90% of all HIV-positive PWID are coinfected with HCV. Although an effective treatment for HCV emerged in late 2013 via the advent of direct acting antivirals (DAA), treatment rates remain exceedingly low among PWID. Our understanding of barriers to treatment among PWID is based largely on studies conducted in the pre-DAA era and, when treatment itself was a barrier; moreover, these known barriers do not account for the changing demographics of PWID in the broader context of the opioid epidemic. Given this innovation in treatment and shifting population dynamics, new research is needed to understand barriers to HCV treatment among PWID, accounting for HIV status and engagement in HIV care. Ultimately, this knowledge will inform interventions to promote HCV treatment uptake among PWID. Aims: We seek to: (1) identify clusters of low HCV treatment penetration in Baltimore, MD and determine if these areas vary by levels of HIV viral suppression; (2) evaluate differences in knowledge of HCV and its treatment by HCV and HIV infection status and other individual and neighborhood-level factors; and (3) compare temporal changes in HCV treatment uptake from 2011-2018 among mono- and coinfected PWID and identify groups with persistent low treatment uptake and associated correlates. Approach: We will accomplish these aims using data from the ALIVE (AIDS Linked to the IntraVenous Experience) study, a community-based cohort of PWID, ongoing since 1988, located in Baltimore, MD. This cohort includes HCV mono-infected and HIV/HCV coinfected PWID, both in and out of HIV care. Aim 1 will identify statistically significant clusters of poor HCV treatment uptake, by census tract, in 2011, 2015, and 2018. To characterize these areas, we will evaluate the extent to which social determinants of health, access to services, and characteristics of HCV-infected individuals explain the clustering. Aim 2 will use a 17-question survey, performed at enrollment and before receipt of HCV counseling, to determine knowledge of HCV and DAAs among participants enrolled 2015-2018, by HCV and HIV status. For Aim 3, we will evaluate temporal changes in the rate of HCV treatment uptake from 2011-2018 by HIV status and HIV viral suppression. Fellowship Information: This study is the dissertation for Ms. Catelyn Coyle, a PhD student in the Department of Epidemiology at Johns Hopkins University. Through a combination of coursework, professional skills development, and mentored research training, the proposed training program will equip Ms. Coyle with the knowledge, skills, and experience to complete the aims of the proposed research and become a successful academic infectious disease researcher.